A major international campaign group has left the Kimberley Process, accusing the international diamond regulatory group of refusing to address links between diamonds, violence and tyranny.

Global Witness's departure on Monday raises questions about whether consumers can be sure the diamonds they buy are not fueling conflicts.

In a statement, Global Witness cited what it called Kimberley Process failures in Ivory Coast, Venezuela and Zimbabwe.

"Consumers have a right to know what they're buying, and what was done to obtain it," said Charmian Gooch, a Global Witness founding director.

"The diamond industry must finally take responsibility for its supply chains and prove that the stones it sells are clean."

The diamond industry, rights groups and 75 countries have worked together as members of the Kimberley Process since 2003 to impose requirements on its members to enable them to certify rough diamonds as "conflict-free" so that purchasers can be confident they are not funding violence.

'Off the hook'

Annie Dunnebacke, a senior campaigner at Global Witness, told Al Jazeera that the rights group was the first to expose the problem of blood diamonds in 1998, and had played an instrumental role in building the Kimberly Process.

"We haven't taken this decision lightly, the KP (Kimberley Process) has achieved certain things, but we feel today it is not achieving its aim in breaking the link between diamonds and violence and human rights abuses," she said.

Dunnebacke said Global Witness's decision to withdraw came after discovering the political will of the countries involved "simply wasn't there".

"We would like to refocus the debate on industry, and that they have largely been left off the hook since the KP was created," she said.

"There is no provision or obligation for industry to take responsibility for the diamonds they buy, for what is in their supply chain.

"We would like to see industry meeting international standards in that regard, and governments enforcing that."

'Blood diamonds'

The Kimberley Process project was born after wars in Sierra Leone and Liberia that were fueled by "blood diamonds".

Partnership-Africa Canada is the only other rights group still in the process.

The departure of Global Witness would lessen the credibility of the Kimberley Process, said Farai Maguwu, head of Zimbabwe's independent Centre for Research and Development, which has monitored rights violations in that nation's diamond trade.

Global Witness was "a strong voice for communities living in diamond producing areas," Maguwu said. "Independent groups like Global Witness are important to ensure rights issues are upheld."

Last month, in a decision Global Witness called "disappointing" at the time, the Kimberley Process agreed to let Zimbabwe trade about $2bn in diamonds from fields where human rights groups say miners have been tortured.

Human Rights Watch has accused Zimbabwean troops of killing more than 200 people, raping women and forcing children to search for the gems in the fields.

Zimbabwe has denied allegations of human rights abuses in the fields.

"Over the last decade, elections in Zimbabwe have been associated with the brutal intimidation of voters," Gooch said on Monday.

"Orchestrating this kind of violence costs a lot of money. The Kimberley Process's refusal to confront this reality is an outrage."